Move toString() to collection classes.

sdk/lib/collection/queue.dart

Index: sdk/lib/collection/queue.dart
diff --git a/sdk/lib/collection/queue.dart b/sdk/lib/collection/queue.dart
index 7bc65cab6fe5a63e7da2e3ae1881d748b6025f0d..76dfe3d34542ec807109b6454496f3dcac7757ff 100644
--- a/sdk/lib/collection/queue.dart
+++ b/sdk/lib/collection/queue.dart
@@ -300,10 +300,9 @@ class DoubleLinkedQueue<E> extends IterableBase<E> implements Queue<E> {
   _DoubleLinkedQueueIterator<E> get iterator {
     return new _DoubleLinkedQueueIterator<E>(_sentinel);
   }
-
-  String toString() {
-    return ToString.iterableToString(this);
-  }
+  
+  // TODO(zarah)  Remove this, and let it be inherited by IterableBase
+  String toString() => IterableMixinWorkaround.toStringIterable(this);
 }
 
 class _DoubleLinkedQueueIterator<E> implements Iterator<E> {
@@ -529,10 +528,9 @@ class ListQueue<E> extends IterableBase<E> implements Queue<E> {
       _modificationCount++;
     }
   }
-
-  String toString() {
-    return ToString.iterableToString(this);
-  }
+  
+  // TODO(zarah)  Remove this, and let it be inherited by IterableBase
+  String toString() => IterableMixinWorkaround.toStringIterable(this);
 
   // Queue interface.